fix QtWheelEvent propagation

as described here
http://www.setnode.com/blog/mouse-wheel-events-event-filters-and-qscrollarea/

sdrgui/gui/valuedialz.cpp

@@ -428,6 +428,7 @@ void ValueDialZ::wheelEvent(QWheelEvent* event)
 
         setValue(m_valueNew);
         emit changed(m_valueNew);
+	event->accept();	
     }
 }